Tough call. If you would have asked me three weeks ago, I would have said Beretta. The grip just seems to melt into your hands and is very comfortable.
Now I have my P2000SK which is equally as good. The ergonomics on the P2K grip are different from the Beretta. The P has finger grooves along with an overall ergonomic shape. Excellent grip for small and average hands.
The grip on my Kimber Ultra Carry II is not too shabby either. Nothing special about it but it is shaped nicely and is comfortable to handle. Mine came with rubber side grips and the rear of the frame is serrated to also improve grip. Effects are minimal, IMO.
The Springfield XD series is not at all shaby. Very basic, not to ergonomic, but comfortable. Haveing an XD has piqued my interests in handling a Glock just to feel the differences in grip angle.
Of all, my HK USP is my least favorite when it comes to grip. However...it is a large frame pistol and I have average hands, so it probably wasn't the best choice. With gloves on though, it's up there with Springfield...comfortable, nothing to write home to mom about.